It is known that reinforcing fillers such as carbon black and silica greatly improve the strength and fatigue properties of elastomeric compounds. It is also known that chemical interactions occur between the elastomer and the filler. Good interaction between carbon black and highly unsaturated elastomers such as polybutadiene (BR) and styrene butadiene copolymers (SBR) occurs due to the large number of carbon-carbon double bonds present in the copolymers. Butyl elastomers may have only one tenth, or fewer, of the carbon-carbon double bonds found in BR or SBR, and compounds made from butyl elastomers are known to interact poorly with carbon black. For example, a compound prepared by mixing carbon black with a combination of BR and butyl elastomers results in domains of BR, which contain most of the carbon black, and butyl domains which contain very little carbon black. It is also known that butyl compounds have poor abrasion resistance.
Canadian Patent Application 2,293,149 teaches that it is possible to produce filled butyl elastomer compositions with improved physical properties by combining halobutyl elastomers with silica and specific silanes. These silanes act as dispersing and bonding agents between the halogenated butyl elastomer and the filler. However, one disadvantage of the use of silanes is the evolution of alcohol during the manufacturing process and potentially during the use of the manufactured article produced by this process. Additionally, silanes significantly increase the cost of the resulting manufactured article.
Co-pending Canadian Patent Application 2,418,822 teaches a process for preparing compositions containing halobutyl elastomers and at least one mineral filler that has been reacted with at least one organic compound containing at least one basic nitrogen-containing group and at least one hydroxyl group and optionally at least one silazane compound before admixing the (pre-reacted) filler with the halobutyl elastomer. According to CA 2,418,822 the elastomers have improved properties, such as tensile strength and abrasion resistance due to the pre-functionalization of the silica with DMAE and/or HMDZ.
Co-pending Canadian Application CA 2,368,363 discloses filled halobutyl elastomer compositions containing halobutyl elastomers, at least one mineral filler in the presence of organic compounds containing at least one basic nitrogen-containing group and at least one hydroxyl group and at least one silazane compound.
Co-pending Canadian Patent Application 2,339,080 discloses filled halobutyl elastomeric compounds containing certain organic compounds containing at least one basic nitrogen-containing group and at least one hydroxyl group enhance the interaction of halobutyl elastomers with carbon-black and mineral fillers, resulting in improved compound properties such as tensile strength and abrasion (DIN).
Filled halobutyl elastomeric compounds according to the present invention utilize phosphines as a novel class of modifiers. The phosphonium modified butyl according to the present invention is ionomeric and therefore possess enhanced affinity towards polar, hydrophilic fillers such as silica. Unlike the amine modifiers known in the cited art, the phosphine modifiers according to the present invention, are involatile and therefore safer to use.